The present invention relates to a fluid for traction drive and more particularly to a fluid for traction drive which contains specified two kinds of compounds as main components and is excellent in traction performance.
A fluid for traction drive is a fluid for use in traction drive devices (devices driven by friction due to rolling contact), such as continuously variable transmissions for automobiles and industrial machines, hydraulic machines and the like. These fluids for traction drive are required to have a high traction coefficient and high stability against heat and oxidation, and further to be inexpensive.
In recent years, extensive investigations on a reduction in the size and weight of traction drive devices have been made particularly in the car industry. Under such circumstances, it is now required for such fluids for traction drive to be used in traction drive devices to be able to withstand use under severe conditions; in particular, to exhibit high performance with stability over a wide temperature range from low temperatures to high temperatures (from about -30.degree. to 120.degree. C.), including a high traction coefficient, relatively low viscosity, high oxidation stability and so on.
However a fluid satisfying the above requirements has not been developed; that is, conventional fluids have various problems. For example, compounds having a high traction coefficient at high temperatures produce a large stirring loss because of their high viscosity and therefore have problems in that the transmission efficiency is low and starting properties at low temperature are not good. On the other hand, compounds having a low viscosity and excellent transmission efficiency are low in the traction coefficient at high temperatures and further have a problem in that as the temperature rises, the viscosity excessively drops, thereby causing troubles in lublication of traction transmission devices.